Internal combustion engines utilizing a volume change among pistons are known in the following documents:
PATENT DOCUMENT 1: Japanese Patent Publication No. 56-159504
PATENT DOCUMENT 2: Japanese Patent Publication No. 59-168223
PATENT DOCUMENT 3: Japanese Patent Publication No. 61-47967
PATENT DOCUMENT 4: Japanese Patent Publication No. 5-7524
PATENT DOCUMENT 5: Japanese Patent Publication No. 6-323103
PATENT DOCUMENT 6: Japanese Patent Publication No. 9-303101
PATENT DOCUMENT 7: U.S. Pat. No. 3,139,871
PATENT DOCUMENT 8: German Patent Application No. 30 38 500
Various techniques of utilizing a periodical change in space between pistons, i.e., inter-piston space, for operation strokes of an engine have actually been employed in pumps and compressors. Internal combustion engines utilizing such techniques are often considered to be similar to pumps or the like in appearance, recalling a relationship of reversible energy direction, e.g., a relationship between a motor and a power generator or between a reciprocating engine and a reciprocating pump. These internal combustion engines are distinctly different from pumps or the like in terms of mechanical engineering in an aspect in which a rotation transmission mechanism for eliminating interference of reverse rotational forces on pistons at rear portions of an explosive combustion chamber in normal rotational forces in order to prevent the reverse rotational forces from being transmitted to an output shaft is needed, and in an aspect in which a large amount of heat generated in an explosive combustion stroke requires particular cooling for, for example, the pistons. Some of known internal combustion engines of this type do not seem to be configured under consideration of the above differences. For example, in such an internal combustion engine, a rotation transmission mechanism in which normal and reverse rotational forces are completely fixed by, for example, gears and which is used only in a pump or a compressor, is applied to an internal combustion engine. Thus, appropriate internal combustion engines of this type have not been obtained yet.
In addition, it is necessary to compress a necessary minimum amount of air or air fuel mixture having a stoichiometric air-fuel ratio to a pressure as high as possible within a knocking limit according to a necessary applied torque in the entire range from a low load to a high load, and to burn the air fuel mixture, in terms of energy efficiency in thermodynamics and of exhaust gas purification. In a general internal combustion engine having a constant compression ratio with a fixed cylinder volume and a fixed combustion-chamber volume, when the amount of intake combustion gas varies, the combustion pressure of the combustion chamber also varies in proportion to the amount of intake air. Accordingly, such an internal combustion engine has a problem in which the combustion pressure and the energy efficiency generally decreases as the amount of intake gas decreases.
A variable stroke mechanism and a movable cylinder head mechanism in a reciprocating engine are known as variable control mechanisms of a combustion-chamber volume. In addition, an EGR technique of recirculating exhaust gas to a combustion chamber so as to reduce the combustion-chamber volume accordingly, is also associated with control of the combustion-chamber volume.